The production of nitrous oxides (hereinafter "NOx") occurs as a result of combustion at high temperatures. NOx is a notorious pollutant, and as a result, combustion devices which produce NOx are subject to ever more stringent standards for emissions of such pollutants. Accordingly, much effort is being put forth to reduce the formation of NOx in combustion devices.
One solution has been to premix the fuel with an excess of air such that the combustion occurs with local high excess air, resulting in a relatively low combustion temperature and thereby minimizing the formation of NOx. A tangential entry fuel nozzle which so operates is shown in U.S. Pat. No. 5,307,634, which discloses a scroll swirler with a conical center body. The scroll swirler comprises two offset cylindrical-arc scrolls connected to two endplates. Combustion air enters the swirler through two rectangular slots formed by the offset scrolls, and exits through a combustor inlet in one endplate and flows into the combustor. A linear array of orifices located on the outer scroll opposite the inner trailing edge injects fuel into the airflow at each inlet slot from a manifold to produce a uniform fuel air mixture before exiting into the combustor.
Premix fuel nozzles of this type have demonstrated low emissions of NOx relative to fuel nozzles of the prior art. Unfortunately, the nozzle experienced durability problems related to severe deterioration of the centerbody as a result of the flame stabilizing within the premixing volume of the nozzle. As a result, the operational life of such nozzles when used in gas turbine engines has been limited.
What is needed is a method of combustion that significantly reduces the tendency of the combustion flame to stabilize inside of the fuel nozzle, and tends to disgorge any flame that does migrate into the mixing zone of the fuel nozzle.